PHP framework - A piece of code in PHP's CI framework is difficult to understand by myself. I hope someone can give me some advice.

/*
 * ------------------------------------------------------
 * Security procedures
 * ------------------------------------------------------
 */

if ( ! is_php('5.4')) // 如果php版本大于等于5.4
{
    ini_set('magic_quotes_runtime', 0);

    if ((bool) ini_get('register_globals'))
    {
        $_protected = array(
            '_SERVER',
            '_GET',
            '_POST',
            '_FILES',
            '_REQUEST',
            '_SESSION',
            '_ENV',
            '_COOKIE',
            'GLOBALS',
            'HTTP_RAW_POST_DATA',
            'system_path',
            'application_folder',
            'view_folder',
            '_protected',
            '_registered'
        );

        $_registered = ini_get('variables_order');
        foreach (array('E' => '_ENV', 'G' => '_GET', 'P' => '_POST', 'C' => '_COOKIE', 'S' => '_SERVER') as $key => $superglobal)
        {
            if (strpos($_registered, $key) === FALSE)
            {
                continue;
            }

            foreach (array_keys($$superglobal) as $var)
            {
                if (isset($GLOBALS[$var]) && ! in_array($var, $_protected, TRUE))
                {
                    $GLOBALS[$var] = NULL;
                }
            }
        }
    }
}

I don’t quite understand what these codes are doing, and what are the benefits of doing so?
I humbly ask all the masters for advice.

Reply content:

/*
 * ------------------------------------------------------
 * Security procedures
 * ------------------------------------------------------
 */

if ( ! is_php('5.4')) // 如果php版本大于等于5.4
{
    ini_set('magic_quotes_runtime', 0);

    if ((bool) ini_get('register_globals'))
    {
        $_protected = array(
            '_SERVER',
            '_GET',
            '_POST',
            '_FILES',
            '_REQUEST',
            '_SESSION',
            '_ENV',
            '_COOKIE',
            'GLOBALS',
            'HTTP_RAW_POST_DATA',
            'system_path',
            'application_folder',
            'view_folder',
            '_protected',
            '_registered'
        );

        $_registered = ini_get('variables_order');
        foreach (array('E' => '_ENV', 'G' => '_GET', 'P' => '_POST', 'C' => '_COOKIE', 'S' => '_SERVER') as $key => $superglobal)
        {
            if (strpos($_registered, $key) === FALSE)
            {
                continue;
            }

            foreach (array_keys($$superglobal) as $var)
            {
                if (isset($GLOBALS[$var]) && ! in_array($var, $_protected, TRUE))
                {
                    $GLOBALS[$var] = NULL;
                }
            }
        }
    }
}

I don’t quite understand what these codes are doing, and what are the benefits of doing so?
I humbly ask all the masters for advice.

If you identify the register_globals status when the PHP version is greater than 5.4, you can see that there are some keywords in the array. The following operations are for security reasons. If register_globals is turned on, it means various variables There is a risk of being injected. For example, if you usually use $_POST to get the parameters passed in the post method, if it is injected, it will become another action, so you need to protect it.

register_globals information can refer to
http://php.net/manual/zh/security.globals.php